It seems that YouTube can be used for more than just entertainment for teens and hobbyists. Check out this link Agent Nets 7 Figure Advance for an interesting article on how an agent used a book trailer on YouTube to attract a book auction with a 7 figure advance.
Author Lois Winston also has her new book trailer up at YouTube - Love, Lies, and a Double Shot of Deception. Apparently, YouTube has an entire section for booktrailers, and it's totally FREE promotion for your book. Have an enterprising child, friend, or husband who likes to tinker with graphics and music? Show your trailer to your agent and you might get a pleasant surprise on your next sale!